The present invention relates to a method for controlling the amount of fuel injected into a direct-injection internal combustion engine. More especially, the invention relates to such a method employed using an injector supplied with fuel under pressure, the opening of said injector being triggered electromagnetically by supplying an electric coil that forms part of the injector with a current spike of predetermined duration.
Electromagnetically operated fuel injectors are well known, as is the method for controlling such an injector mentioned hereinabove (see, for example, U.S. Pat. No. 5,381,297). It is known that such an injector comprises a needle that can move under the action of an electromagnetic field developed by an electric coil supplied with a suitable current, between a position in which one end of this needle closes off an opening pierced in the seat defining a passage for a fuel to be injected into an internal combustion engine cylinder and a position in which the needle uncovers this opening to allow such injection. At rest, the needle is pressed against its seat by a preloading spring and by the pressure of the fuel let into the injector. To overcome this load, and allow the injector to open, it is necessary for the coil to be supplied fleetingly with a strong current, of the order of some ten amps for example, the current spike thus applied being followed by the application of a lower current holding the injector open for a time which is modulated according to the amount of fuel to be injected.
When such an injector is used to supply gasoline to a cylinder of a direct-injection internal combustion engine, it is currently desirable to have the possibility of adjusting this amount of fuel in a wide range. Indeed, when such an engine is operating at light load with a fuel-lean and stratified air/fuel mixture, the amount of gasoline to be injected needs to be very low. By contrast, at high speed and full load, a great amount of gasoline needs to be injected into the engine in a very short time, shorter than 5 ms at 6000 rpm. The ratio of the extreme fuel flow rates, or xe2x80x9cdynamic rangexe2x80x9d of the injector needs therefore to be very high, advantageously of the order of 20.
In order to get close to this value, it has been proposed for the pressure of the gasoline delivered to the injector to be increased when the injector needs to deliver a great deal of gasoline. Thus, for example, the injector is supplied with gasoline at a pressure of 50 bar for small amounts of gasoline to be injected, and at 110 bar for higher amounts. In this way it has been possible to obtain a dynamic range of about 15, which is still considered to be insufficient.
It is therefore an object of the present invention to provide a method for controlling the amount of fuel injected into a direct-injection internal combustion engine by an injector with a high dynamic range, typically of the order of 20.
This object of the invention together with others which will become apparent from reading the description which will follow, is obtained using a method for controlling the amount of fuel injected into a direct-injection internal combustion engine by an injector supplied with fuel under pressure, the opening of said injector being triggered electromagnetically by supplying an electric coil that forms part of the injector with a predetermined current spike, this method being notable in that said duration of said current spike is an increasing function of said fuel pressure.
As will be seen in detail further on, this method makes it possible to widen the range of values of amounts of fuel injected, both at the small quantity end and at the highest quantity end.
According to another feature of the method according to the invention, the duration of said current spike is also an increasing function of the duration of a predetermined injector-open time.